Hitherto, there has been proposed a technical approach for controlling an operation of a leg when a robot travels such that a vertical component of the velocity of a foot approximates zero before landing so as to ease an impact to the leg and the like when the foot lands on a floor. With this arrangement, when, for example, a bipedal mobile robot runs by repeating a floating period during which both legs are in the air and a one-leg supporting period during which the robot is supported by one of the legs, a desired foot height of the right foot is set such that it reaches zero immediately before the floating period is switched to the one-leg supporting period, as shown in FIG. 19(a).
There has been proposed another technical approach in which a compliance mechanism for reducing an impact to a leg and the like when a foot lands on a floor is provided, and a desired trajectory of a foot is set, considering the deformation of the compliance when a foot lands on a floor. With this arrangement, if, for example, while the bipedal mobile robot is running, a desired floor reaction force suddenly increases from zero immediately after the floating period is switched to the one-leg supporting period and maintained at a constant value thereafter, and then suddenly decreases to zero immediately before the next floating period, as shown in FIG. 19(b), then the amount of deformation of the compliance mechanism attributable to the desired floor reaction force is predicted to change as shown in FIG. 19(c). Further, the desired foot height shown in FIG. 19(a) is corrected and reset as shown in FIG. 19(d) so as to compensate for the amount of deformation.
However, if, for example, the desired foot height (desired foot trajectory) as shown in FIG. 19(d) is set, then an inconvenience described below will occur.
Immediately after a leg moves to a ground-contacting period, an actual floor reaction force starts to develop with a delay with respect to a desired floor reaction force, as shown in FIG. 19(e), leading to a danger in that a foot is not adequately decelerated and the actual floor reaction force and eventually an impact to the robot at landing temporarily become excessive.
In addition, a time delay may take place in the deformation of the compliance mechanism due to a response delay of an actuator acting as a motor of a leg, a transmission delay in a driving force transmission system, and a response delay due to a deflection in a leg mechanism, leading to a possibility of deterioration in follow-up of an actual floor reaction force acting on a foot (=a floor reaction force measured by a 6-axis force sensor or the like provided on a foot joint) to a desired floor reaction force. For instance, as shown in FIG. 19(e), if an actual floor reaction force acting on a foot changes with a delay in relation to the desired floor reaction force shown in FIG. 19(b) after the foot shifts from a non-ground-contacting period to a ground-contacting period, then a finite actual floor reaction force may remain (unloading may deteriorate) despite that the actual floor reaction force should have been zero because of the foot having left a floor as the period shifted to the next non-ground-contacting period. This may cause a toe or the like of the foot to be caught on a floor surface, leading to a possibility of a motion of the robot being disturbed at least temporarily thereafter.
Accordingly, an object of the present invention is to provide a legged mobile robot that permits improved follow-up of an actual floor reaction force to a desired floor reaction force and stable control of a motion thereof, and a control program for the same.